manifold to operate the command sequencing and canopy jettison systems. 3. To the 0.30-second delay cartridge-actuated initiator (aft seat only) on the RH ballistic manifold. Gas from the initiator passes to the RH inlet of the catapult manifold valve to initiate the catapult. 4. To the breech of the shoulder harness reel, where it fires the impulse cartridge to pull the seat occupant into the correct position for ejection. 5. To the thermal batteries. 6. Via a check valve to the 0.75-second delay cartridge-actuated initiator on the LH ballistic manifold. Gas from the initiator passes to the LH inlet of the catapult manifold valve to initiate the catapult. 7. If the seat (F/A-18D only) is command ejected (i.e., the ejection control handle on the other seat has been pulled), gas from the command sequencing system enters the RH seat initiating system through the inboard connector of the command sequencing quick-disconnect on the RH ballistic manifold, and operates as described in 1 through 6 above. On the forward seat only, gas pressure also enters the outboard connector of the command sequencing quick- disconnect and is passed to the catapult manifold valve to initiate the catapult. This gas pressure is also piped, via a check valve, to the shoulder harness reel and thermal batteries. Gas from the LH cartridge is piped as follows: 1. To the thermal batteries. 2. To the 0.75-second delay, cartridge- actuated initiator on the LH ballistic manifold. Gas from the initiator passes to the LH inlet of the catapult manifold valve to initiate the catapult. Gas from the delay initiator is piped to the ejection gun initiator via the manifold valve. Gas pressure developed by the initiator passes down the catapult to operate the ballistic latches, retaining the IMP lanyard end fittings. As the pressure increases within the catapult, the catapult piston rises, releases the top latch, and begins to move the seat upwards. Further movement of the piston uncovers the catapult secondary impulse cartridge, which is fired by the heat and pressure of the ejection gun initiator gas. Staggered firing of the catapult cartridges provides a relatively even increase in gas pressure during catapult stroke to eliminate excessive g-forces during ejection. As the seat goes up the guide rails: 1. The IMP lanyards begin to withdraw. 2. Personal services between seat and aircraft are disconnected. 3. The emergency oxygen supply is initiated. 4. The URT-33A beacon is activated. 5. The leg restraint lines are drawn through the snubbers and restrain the occupants legs to the front of the seat bucket. When the leg restraint lines become taut, the special break ring incorporated in each leg line fails, and the lines are freed from the aircraft. Forward movement of the legs is prevented by the lines being restrained by the snubbers. Near the end of the catapult stroke, the IMP lanyards become taut and operate the firing mechanisms. Gas pressure from the IMP cartridge passes: 1. To the start switch plungers. Closure of the start switches commences sequencer timing. 2. To the barostatic release unit release piston (from the RH IMP only). 3. To the pitot mechanisms to deploy the pitot heads. 4. Via the LH ballistic manifold and trombone tube to the underseat rocket motor. The rocket motor ignites, sustaining the thrust of the catapult to carry the seat clear of the aircraft. SEQUENCER MODES Electronic sequencer timing (table 5-2) commences when the start switches close. Mode selection is dependent on altitude and airspeed parameters. (See figure 5-35.) All modes. The start switches close after approximately 39 inches of seat travel and, after 0.04 second, the drogue deploys onto the bridle to stabilize and decelerate the seat. Mode 1, low speed - low altitude. The drogue bridle is released,   the parachute deployment rocket motor fires to deploy the personnel parachute, and the harness release system operates to free the occupant from the seat. The occupant is momentarily held in the seat bucket by the sticker straps. Modes 2, 3, and 4, medium and high speeds - low altitude and all speeds - medium altitude. The parachute deployment rocket motor fires to deploy the parachute, the drogue bridle is released, and the harness release system operates to free the occupant from the seat. The occupant is momentarily held in the seat bucket by the sticker straps. 5-35